1-aminopropanediol-2,3 which is useful as a starting material for non-ionic X-ray contrast agents, is an industrially interesting product (for example, see Belgian Pat.No. 855,580), and the demand therefore recently has increased.
Hitherto, it has typically been produced by a reaction of glycidol with ammonia.
For example, a process for the preparation of 1-aminopropanediol-2,3 which comprises a reaction of glycidol with 25% aqueous ammonia and a final distillation under reduced pressure conditions to obtain the refined product, is disclosed in "Ber. Deutsche Chem. Ges.", Vol. 32, pages 750-757, 1899 (L. Knorr et al).
Furthermore, a process for the preparation of 1-aminopropanediol-2,3 which comprises a reaction of glycerine-alpha-monochlorohydrin with 25% aqueous ammonia and a final distillation under reduced pressure conditions to obtain the refined product, is disclosed in "Journal of Organic Chemistry", Vol. 27, pages 2231-2233, 1962 (K. Baum et al).
Still further, Japanese Patent Examined Publication (Kokoku) No. 37,342/1990 (corresponding to U.S. Pat. No. 4,356,323), Japanese Patent Unexamined Publication (Kokai) No. 161357/1981 (corresponding to U.S. Pat. No. 4,360,697), and Japanese Patent Examined Publication (Kokoku) No. 37,343/1990 (corresponding to U.S. Pat. No. 4,358,625) teach that 1-aminopropanediol-2,3 can be effectively prepared by a reaction of glycidol with liquid ammonia under pressurized conditions.
The above described disclosures disclose only the yield of 1-aminopropanediol-2,3 and the reaction conditions, such as a molar ratio between starting materials, reaction temperatures, reaction pressures, the amount of water to be used together with liquid ammonia, etc.
However, it has been known to the present inventors that 2-aminopropanedio-1,3, which is an undesirable impure component, and which can not be reduced to less than 0.30% by weight by the prior techniques without an improvement, is by-produced, even though in a minor amount, in the preparation of 1-aminopropanediol-2,3.
Heretofore, commercially supplied 1-aminopropanediol-2,3 has contained from more than 0.30 to 0.50% or more (based on the weight of 1-aminopropanediol-2,3) of 2-aminopropanediol-1,3.
It is noted that 2-aminopropanediol-1,3 adversely affects the use described above, even though it is present in a relatively minor amount.
More specifically, for example, there has been a problem such as low yields of final product in the case that the non-ionic X-ray contrast agents are manufactured using 1-aminopropanediol-2,3 containing large amounts of 2-aminopropanediol-1,3.
Accordingly, it has been desired that 1-aminopropanediol-2,3 containing small amounts of 2-aminopropanediol-1,3 would be developed.
As the result of the background described above, the present inventors have earnestly investigated to prepare a highly purified 1-aminopropanediol-2,3 containing small amounts of 2-aminopropanediol-1,3, which can be obtained by distilling with a distillation column having low pressure loss from a crude 1-aminopropanediol-2,3 containing more than 0.3% of 2-aminopropanediol-1,3 (based on the weight of 1-aminopropanediol-2,3).